Bacillus thuringiensis (Bt) produces an insect toxin designated as .delta.-endotoxin. It is synthesized by the Bt sporulating cell. The toxin, upon being ingested in its crystalline form by susceptible insect larvae, is transformed into biologically active moieties by the insect gut juice proteases. The primary target is insect cells of the gut epithelium, which are rapidly destroyed.
The reported activity spectrum of Bt covers insect species within the order Lepidoptera, many of which are major pests in agriculture and forestry. The activity spectrum also includes the insect order Diptera, which includes mosquitoes and black flies. See Couch, T. L., (1980) "Mosquito Pathogenicity of Bacillus thuringiensis var. israelensis," Developments in Industrial Microbiology 22:61-76; Beegle, C. C., (1978) "Use of Entomogenous Bacteria in Agroecosystems," Developments in Industrial Microbiology 20:97-104. Krieg, et al., Z. Ang. Ent. (1983) 96:500-508, describe a Bt isolate named Bacillus thuringiensis var. tenebrionis, which is reportedly active against two beetles in the order Coleoptera. These are Colorado potato beetle, Leptinotarsa decemlineata, and Agelastica alni.
In our parent application, Ser. No. 714,790, we disclose a novel Bt isolate active against Coleoptera. There is no disclosure of activity against the cotton boll weevil (Anthonomus grandis), the Colorado potato beetle (Leptinotarsa decemlineata), the alfalfa weevil (Hypera postica) or the corn rootworm (Diabrotica longicornis).
We have also subsequently discovered that this Bt isolate is not active against all Coleoptera tested. See Table 1, infra.